2000 CLK320 engine won't shut off with headlights on
 

This is a weird problem that I have not found any info for online. If the car is running with the headlights on, and you turn off the ignition switch, leaving the lights on, the engine won't shut off. You have to put the key back in the ignition and then turn off headlights then Pull out key to shut off engine. What could that be?

Any work just before the problem?

Does this car have remote start / aftermarket radio / aftermarket alarm ? Lots of odd things can occur.

Also, mice can chew wiring and cause all sorts of odd problems.

Simple solution: Turn off headlights before turning off engine.